For some time, known flush toilets flushed with flush water supplied from a flush water source to discharge waste have included those in which, as set forth for example in Patent Document 1 (Japanese Patent Unexamined Publication No. 2016-501326), a single rim spout port is disposed on the rear side of a rim, and flush water is spouted forward from this rim spout port to form a circulating flow.
In conventional flush toilets of this type, at the back portion of the bowl the curvature radius of a curved surface in a lower connecting surface connecting the top edge of a waste receiving surface and the inside edge of a shelf, and the curvature radius of a curved surface connecting the outside edge of the shelf and the bottom end of a rim, are both set to be relatively large. The slope angle of the shelf relative to a horizontal plane is also set to be relatively large.
In the conventional flush toilet set forth in Patent Document 2 (Japanese Patent Unexamined Publication No. 2015-196960), a first rim spout port is formed slightly to the rear side of the side center portion of the bowl, and a second rim spout port is disposed on the rear side of the bowl, such that flush water is spouted toward the front from this first rim spout port and second rim spout port, respectively.
In the rear portion of the bowl in such conventional flush toilets, as well, the curvature radius of the curved surface in the connecting surface connecting the top edge of the waste receiving surface and the inside edge of the shelf are set to be relatively large.
In the conventional flush toilets set forth in the above-described Patent Documents 1 and 2, waste adhering to the rear region inside the bowl is flushed out by flush water reaching the rear region inside the bowl after rim spout water spouted forward from the rim spout port has circulated in the front region inside the bowl.
However, in the above-described conventional flush toilet set forth in Patent Documents 1 and 2, when rim spout water spouted forward from the rim spout port reaches the rear region inside the bowl after circulating in the front region inside the bowl, the force of the flush water is weakened. The problem thus arises that in some cases the rear region of the bowl, to which waste easily adheres, cannot be sufficiently washed down.
In recent years, with the diversification of flush toilet designs, there has been a growing need to plan for visual simplicity in the appearance of the toilet main unit bowl interior or the rim inside perimeter side, by placing items such as the rim spout port or the rim conduit relative to the rim so that the rim spout port or the upstream side rim conduit is invisible to the user, and by designing so that water is spouted rearward from a single rim spout port.
However, in such a flush toilet for spouting water rearward from a rim spout port, the issue is how to increase flushing performance while limiting the volume of flush water required for flushing, so as to reliably wash off the rear region of the bowl where waste can easily adhere.